1. Field of the Invention
The present invention relates to a pressure sense recognition control system in which a pressure sensor is attached to the hand of an intelligent robot, the manipulator remote control system, the bottom of a movable robot foot, and so on, to make the hand, manipulator or foot recognize senses similar to those of the human being such as sense of touch, pressure, slippage, hardness, or the like; and controls the hand, manipulator or foot based on that recognition. In the specification, the term "pressure sense" is used in a broad sense and should be defined to include tactile or tactual sense.
2. Description of the Prior Art
Forces applied to the hands or the feet of robots, which work in place of human beings, are three-dimensional and have a certain distribution. An amount and a direction of the applied force and a distribution of the force on the pressure surface varies as the hands (manipulators) or feet move. A human being senses not only this force, i.e., pressure, but also a combination of touch, slippage, hardness, and so on, as pressure sense or tactile or tactual sense. With this in view, a machine requires these senses to control the hands and feet to the high degree equivalent to those attained by human beings. Of these senses, it is required to sense a pressure in a three-dimensional manner and to recognize a distribution of the pressure as the most basic sensing.
Here, the three-dimensional sensing of a pressure means the sensing of three components of a force in three directions in the rectangular coordinate system including the sensing of a vertical component force on a pressure surface and the sensing of two-directional component forces on the pressure surface. It is also desired to additionally sense moments in the three directions resulting from hand or foot operations.
Sensors as shown in FIGS. 1, 2, 3A and 3B have been proposed as sensors sensing in the three directions. These prior art sensors consist of an elastic member 1 such as elastic ring, cross leaf spring, elastic block or the like and a plurality of strain gauges 3 adhered to the elastic member 1 in the respective directions. Since the size of the sensor is substantially equal to or larger (e.g., the length of each edge of the sensor is approximately from 100 mm to 200 mm) than the object gripped by the hand, the sensor is not attached to the pressure surface of the hand or foot, but is merely attached to an ankle or wrist 5 only to detect an entire working force of the hand or foot. As a result, these prior art sensors do not sense touch, slippage and hardness. Accordingly, it is necessary to provide a special sensor separately if sense information of touch, slippage or hardness is required. However, since such a special sensor is also relatively large and provides no more than general sense information in areas corresponding to the palm of the hand resulting from the differences or the like in a space to which a pressure is applied or a position for sensing. The sensor cannot provide delicate sense information from portions corresponding to fingers.
As described above, one of the distinctive features of the human senses is the capability of recognizing a pressure distributed over a surface. The pressure surface of a robot, etc., is of a limited size and if the gripped object is not a flat surface or when a hand or foot moves in a certain manner, a force applied to the pressure surface will not be uniform. For that reason, it is necessary to recognize the sense of pressure in a distributed state. As a result of that recognition, an area of the pressure surface, a center of the working force and changes thereof with time are sensed.
Sensors as shown in FIGS. 4A, 4B, 5 and 6A-6D have been proposed as having the senses of recognizing the distribution of that applied force. The sensor shown in FIG. 4A has a silicone rubber cord 15, which is made of electrically conductive rubber, and a metal electrode 17. An area of the contact between the surface of the rubber cord 15 and the electrode 17 varies in accordance with a pressure applied to the cord 15, so that a resistance value is varied.
In the sensor shown in FIG. 4B, the metal electrodes 17 are laid across silicone rubber cords 15 in lattice form and a scanning system in ITV (industrial television) system is used for detection.
In the sensor shown in FIG. 5, points of a plurality of small pins 19 move upward and downward in the vertical direction following the shape of a three-dimensional object being detected and a differential coil and a hole element (not shown) cooperate to detect and recognize the shape of the three-dimensional object.
The sensors shown in FIGS. 6A to 6D use electrically conductive rubber etc. and can be applied as force sensing sensors in robots.
The sensor shown in FIG. 6A has a combination of a conductive rubber sheet 7 and metal electrodes 8. Insulating electrode supports 9a are arranged on a base plate 9 in distributed locations and the metal electrodes 8 are disposed on the top of the electrode support 9a. Each of resilient members 9b, e.g., sponge rubber member, is placed between the electrode supports 9a and the conductive rubber sheet 7 is adhered to or disposed on the top of resilient and conductive member 9b. It is easily understood that the resilient member 9b in the portion receiving a load F is compressed downward in the drawing and the deflection is detected by an electrical contact between the conductive rubber sheet 7 and the electrode 8, so that the location and distribution of load F are determined.
In FIG. 6B, a plurality of cylindrical electrodes 8 are fabricated in a distributed manner over the surface of the base plate 9, which is disposed under the conductive or pressure sensitive rubber sheet 7 as the resilient sheet. A distribution and a position of load F is detected by the electrode 8 which is electrically in contact with the conductive rubber sheet 7 at a position to which load F is applied.
In the sensor shown in FIG. 6C, a series of the conductive rubbers 7a are embedded in the form of row into the bottom surface of the insulating rubber sheet 7. The strip electrodes 8 are attached to the top surface of the insulating substrate 9 in the form of column in opposition to the conductive rubbers 7a. The electrode 8 and the conductive rubber 7a are in electrical contact at the junction of the column and the row corresponding to the portion of the insulating rubber sheet 7 where load F is applied, so that the load distribution can be determined from the distribution of contact points.
FIG. 6D shows the sensor in which a thin metal plate made of beryllium copper or foil etc. is used for the strip electrode 8a. Here, use is made of the elasticity of the electrode 8a itself or the elasticity of an insulating cover 8c covering the strip electrode 8a. A base 9, to which this combination of the members 8a and 8c is attached, is made of metal, for example. A peripheral portion 9c of the base 9 forms an electrode surface. An insulating plate 8d insulates the foil electrode 8a from the base 9. If a plurality of foil electrodes 8a are arranged along the base 9, a load distribution is detected, because the combination of the electrodes 8a and the insulating cover 8c is deflected when a load F is applied to the combination so that the foil electrode 8a electrically contacts the electrode surface 9c of the base 9.
However, all these conventional sensors sense only in the direction perpendicular to the sensor pressure surface. In order to precisely detect the distribution, each sensor module must be small, but structural limits prevent the modules from being made small enough. The sensors described above can only be used for contact detection and pressure surface detection, i.e., as contact sensing sensors, and are inadequate as pressure sensor substitutes for human senses due to their use of conductive rubber as the principal detection mechanism. Conductive rubber has a non-linear characteristics to applied force and a narrow dynamic range. Consequently, conventional sensors do not permit sense recognition control close to that achieved by the human senses.
FIG. 7 shows an octagonal stress ring sensor conventionally used as a ring type loadcell for detecting three-directional force components. As strain gauges, resistance wire gauges 23-26, 27-30 and 31-34 are adhered to the two vertical side surfaces, the surface of the inner periphery and the six surfaces (excluding a pressure surface 21 and a substrate 22) on the outer periphery of a metal octagonal ring 20 in a manner that the sets of the gauges 23-26, 27-30 and 31-34 detect each of the three-directional components independently. The strain gauges 23 and 26 and 24 and 25 are adhered to the two vertical pressure surfaces on the outer periphery of the octagonal ring and to the two vertical surface of the inner periphery of the ring, respectively, so that a vertical force component Fz in the vertical direction z perpendicular to the pressure surface 21. The strain gauges 27-30 are adhered to the four diagonal surfaces on the outer periphery of the octagonal ring to detect a horizontal force component Fx in the horizontal direction x of the horizontal force applied to the pressure surface 21. The strain gauges 31-34 are adhered to both vertical side surfaces of the ring, at the same angle as the outer diagonal edges of the octagonal ring, and are positioned at an optimum position, which is substantially at the center between the inside and outside edges of the ring, to detect a horizontal force component Fy in the direction y of the horizontal force applied to the pressure surface 21.
The three-directional force component sensors detect a force in the form of component forces in the fundamental rectangular coordinates system, i.e., in the form of the three-directional components Fx, Fy and Fz, as shown in FIG. 7. An amount and a direction of the force can be obtained by calculating component force equations for vectorically adding the three component forces. Furthermore, a force in any direction desired can be obtained.
The simple resolution and composition of a force is a major feature of the three-directional component force sensors.
The octagonal stress ring sensor shown in FIG. 7 is used for detecting components of three-directional force, but has the following disadvantages, so that this ring sensor is especially inadequate when the ring sensors are arranged in the form of a two-dimensional array in order to detect a load distribuion distributed over the two-dimensional surface. The disadvantages follow:
(1) It is difficult to reduce a sensor size, since a plurality of strain gauges are adhered to the surfaces in various directions of the ring body.
(2) Sensing characteristics are not stable because the strain gauges are adhered to the ring and the adhered layer produces creep.
(3) A large interference output is produced, depending upon the adhered positions of the strain gauges.
(4) The fabrication of the sensor is relatively difficult. It is particularly difficult to adhere the strain gauges to the inner periphery of the ring.
(5) The sensor does not fit to mass-production and accordingly the sensor is expensive.
On the other hand, in order to realize a robot hand having advanced pressure sensing functions that resemble, as closely as possible, the level of pressure sensing functions in the palm and finger of the human hand, pressure sensors of the robot hand must sense three-directional component forces and a plurality of sensors must be arranged in a plane array manner at a high density, so that the distribution of the applied force, the center of that force and the resultant force that works at the center are obtained accurately. The following performances are required as a pressure sensor for those purposes.
(a) One load detecting unit must be extremely small having dimensions of several millimeters or less. Units in one distributed-load detector must be integrated at the highest possible density.
(b) Component forces of a load must be detected separately without mutual interference.
(c) A relationship between detection output and load must be linear. There must be no hysteresis error in measurement. A dynamic range, i.e., measurement range, must be wide.
(d) The load distribution detector itself must have a high rigidity, so that the detector is not deformed and the load distribution does not change when a load is applied.